The present invention relates to a power generating apparatus performing electric power generation or the like by a Rankine cycle using a heat source such as a hot-spring or subterranean heat source. The present invention also relates to a method of operating such a power generating apparatus.
In recent years, the need and market for small-sized electric power generation have been growing with the spread of energy conservation and with the enactment of the Act on Special Measures Concerning the Procurement of Renewable Electric Energy by Operators of Electric Utilities. In this trend, attention has been paid to a binary electric power generation system using a low-boiling point working medium and hence capable of utilizing a low-temperature heat source not higher than 100° C. such as a heat source obtained from a hot spring, engine exhaust heat, plant exhaust heat, and solar heat. The binary electric power generation system uses a Rankine cycle as a heat cycle and therefore needs a hot heat source for evaporating a working medium and a cold heat source for condensing the evaporated working medium.
As a cold heat source, ground water, tap water, river water, or the like is used, and as a cooling device, as cooling tower, a chiller, or the like is used. Particularly, organic binary electric power generation using a low-boiling point organic working medium, e.g. HFC245fa, is receiving attention as an epoch-making electric power generation method capable of using a heat source having an even lower temperature by utilizing the evaporation and condensation characteristics of a low-boiling point organic working medium.
FIG. 5 shows a conventional general binary electric power generating apparatus 100. In FIG. 5, a closed-loop circulation path 102 through winch a working medium circulates is provided with an evaporator 104, an expander 106, and a condenser 110. The expander 106 is connected to an electric power generator 108 through a driving shaft. In the evaporator 104, a working medium w exchanges heat with a heating medium h and evaporates by absorbing heat from the heating medium h. The working medium w increased in pressure by evaporation enters the expander 106. In the expander 106, the working medium w adiabatically expands and drives the electric power generator 108 by the expansion force to perform electric power generation. After adiabatically expanding, the working medium w exchanges heat with a cooling medium in the condenser 110 and is cooled to condense by the cooling medium. The condensed working medium w is sent to the evaporator 104 by a circulating pump 112.
The binary electric power generation can generate electric power even with a low-temperature heat source, and on the other hand, needs a condensing step using a cold heat source because the binary electric power generation uses a heat cycle in which a working medium circulates through a closed loop. The condensing step is generally a step in which a working medium and cooling water are allowed to exchange heat with each other by using a heat exchanger to condense the working medium, and the condensed working medium is sent to an evaporator by a liquid pump. In many cases, around water, river water, tap water, or the like is used as a cold heat source, and a cooling tower, a chiller, or the like is used as a device for cooling the cold heat source. It is, however, difficult to procure a large amount of water, and a large pumping power is required to supply a large amount of cooling water, which causes the real effective electric generation to be reduced to as considerable extent. In addition, the use of river water is accompanied by the problem of water rights. The use of tap water increases the water bill. The use of a cooling tower increases the electric bill.
Japanese Patent Laid-Open Publication No. 2011-214430 (Document 1) discloses a condensing mechanism for use in as binary electric power generating apparatus. In the condensing mechanism, a working medium liquid lowered in temperature by being cooled in a utilization-side heat exchanger is used as a cooling medium for cooling another working medium in a condenser. That is, the working medium liquid liquefied in the condenser is distributed into two systems, i.e. a flow path leading to an evaporator, and as flow path leading to the utilization-side heat exchanger, and the working medium evaporated by absorbing heat in the evaporator and the working medium cooled in the utilization-side heat exchanger are brought into direct contact with each other in the condenser to exchange heat therebetween.